The Coefficient of Multiple Determination (R2), with Two Independent Variables

The coefficient of multiple determination (R2) , with two independent variables is________.

A) the amount of variation explained by X 1 plus the amount of variation explained by X 2, after controlling for the effect of X 1 .
B) the amount of variation explained by X 1 minus the amount of variation unexplained by X 2 .
C) the total variation in Y minus the amount unexplained by X 1 after controlling for X 2 .
D) the sum of all explained and unexplained variation in X 1 and X 2.